3

In common cycling parlance, 53/39 is referred to as "standard" gearing for road cranksets, and most mechanics or experienced cyclists will understand that if you say you have a "standard crankset", you have a 53/39.

Why is this the case? Who or what caused cycling to specifically adopt 53/39 as "standard" (rather than 52, 51, 50, etc)?

Most bikes nowadays ship with a compact crankset, since manufacturers recognize that the majority of cyclists have difficulties turning over a 53T chainring. However, that only explains why 53/39 is not shipped as standard equipment on most bikes, it doesn't explain how 53/39 came to be referred to as "standard".

As to the "ego/testosterone" explanation, that explains why some cyclists upgrade from compact cranksets. However, there are cyclists that are more than capable of turning a 53T chainring and, therefore, their reasoning for using a 53T does not involve ego/testosterone/posturing. Additionally, this explanation doesn't really explain why 53T is the "standard" big ring, rather than 54T or 55T.

A comment on a previous question sparked this (apologies to that user as I can't seem to find their comment now).

  • I would say it mostly has to do with tradition. You could get basically the exact same gear range using 54-40 or 52-38. Now that we have things like 11 tooth cogs, it makes little sense for non-pro riders to have a 53 tooth chainring since most people can't push it at a reasonable cadence. This is why compact (50-34) is becoming more popular. Gets rid of the hard gears you don't have the power to push and gives you easier gears for getting up the hills, since again, you don't have as much power as the pros. – Kibbee Jun 8 '16 at 15:18
  • 5
    One common standard for cranksets is 130mm BCD. The smallest inner chainring you can use with 130 BCD is a 39. I believe (but this part is a guess, which is why it's not given as an answer) that the 52 or 53 was chosen so that with the common cogs on a cassette back when 130 BCD was established as a standard, there would be relatively little overlap and a reasonable range of gearing. – R. Chung Jun 8 '16 at 15:24
  • 2
    @R.Chung +1 you should post that as an answer. I would add that smaller BCDs weren't used to to keep chain ring flex down, while keeping things light. Now that newer processes (e.g., hollow chain rings) give a super stiff platform, we are seeing smaller BCDs again (e.g., semi-compact). As a historical note some 1940's randonneur setups had very small BCD (e.g., 70 mm) so they could have a large difference in the chain rings (e.g., 28/48) as the cassettes had fewer gears and cassettes didn't have ramping to facilitate shifts between large tooth jumps. – Rider_X Jun 8 '16 at 16:20
  • 1
    Technically you can get a 38 tooth 130 BCD chainring although the amount of metal between the edge of the chainring and the mounting holes gets really small. – Kibbee Jun 8 '16 at 18:09
  • 2
    The next question would be, why 130 (or 135) mm BCD is the standard? It is already a step down from older 144mm standard. And why 53/39? It gives one spot per rotation where the teeth are aligned, where 52/39 would give four. – ojs Jun 8 '16 at 19:15
6

There's a short answer to your question and a longer fuller answer. The short answer is that a common standard for road cranksets is 130mm BCD (bolt circle diameter). The smallest inner chainring you can use with 130 BCD is a 39 (as Kibbee has said, technically you can get a 38 tooth 130 BCD chainring although that doesn't leave much metal between the lower edge of the teeth and the mounting holes). Front derailleurs and rear derailleurs can handle a change in chainring size of perhaps 13 or 14 teeth smoothly and reliably without a problem; larger differences than that can be handled but usually not quite as crisply or reliably. That's why larger front chainrings are often 52 or 53.

Some bikes with triple chainrings can use a much smaller BCD. The old TA Cyclotourist crankset favored by randonneurs could use a small chainring of 24 teeth. However, when the BCD is very small the chainrings must be stronger to prevent warping since there is so much distance from the teeth to the mounting holes at the crank.

Track bikes use a 144 BCD because track riders often use large chainrings (and, of course, only a single ring in a fixed gear set-up).

A relatively recent standard is 110 BCD cranksets that permit a small chainring of 34 teeth. This is often paired with a larger chainring of 50. That is a difference of 16 teeth, which is right on the edge of smooth and reliable shifting with current chainring and derailleur designs. As Rider_X has noted, this recent standard was enabled by new designs that allow for stiff chainrings.

So the BCD determines the smallest chainring that can be used, while the derailleurs put a limit on the largest increase in teeth from small to large chainring that can be handled smoothly and reliably.

Note that two different chainring-cog combinations may have the same gear ratio (for example, a 48-24 and a 36-18 both would have a gear ratio of 2.0). If they have the same gear ratio, then at the same bike speed, your cadence would be the same. Since the bike speed is the same, the power reaching the ground must be the same. So gear ratio is the same, speed is the same, cadence is the same, power is the same -- but chain tension will be different. At the same cadence, say 60 rpm for simplicity, the chainring will make one complete revolution per second. That means that a 48 tooth chainring will move the chain 48 links (or 24 inches) per second, while a 36 tooth chainring will move the chain 36 teeth (or 18 inches) per second. Since the same power must travel from the crank to the rear wheel, the force transmitted through the chain must be higher for the slower moving chain. As an aside, this happens to have been the way that one bicycle power meter worked (the Polar chain speed and tension power meter): it had a sensor to measure chain speed, and another to measure chain tension.

  • 1
    Hmm. I'm really disappointed with this answer; it's just not up the the standard you usually maintain (did you know you have the highest per-answer average score on this site for regular users?). From my point of view, it doesn't answer the meat of the question Why is this the case? How did 53/39 become the standard? – andy256 Jun 9 '16 at 4:54
  • Again, that 53/39 is "the standard" should be established/proven somehow – gaurwraith Jun 9 '16 at 8:25
  • @andy256 Yeah, I'm not quite satisfied with that answer either (and I didn't know the other thing). I'm still doing some research on it. I may edit it when I get a better handle on it. gaurwraith: we know that 130BCD is a standard, and we know that the 39 tooth chainring is usually the smallest that can be used there. Is your question about the 130BCD (and thus the 39 chainring) or about the 52 or 53 chainring? – R. Chung Jun 9 '16 at 13:28
  • 2
    @altomnr Well, 130BCD really began as a Shimano standard. Campagnolo uses 135, so 130 is a reflection of the dominance of Shimano in the OEM component market. – R. Chung Jun 9 '16 at 14:57
  • 1
    Ah, gotcha - didn't realize that Shimano were the originators of 130BCD...makes sense, given their dominance. Campy's 135BCD might explain why 39t is the small ring within "standard" gearing, since that might be the smallest ring you can fit on 135mm (38t barely fits on 130mm)? That's pure conjecture... – Altom Jun 9 '16 at 15:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.